If it`s anything like my Skoda then £400 is cheap for a full system. Recently my front pipe went. In the front pipe the Cat is incorporated. It can`t be unbolted, it is part of the pipe. No problem i thought. I went round all the exhaust places, German and Swedish, EuroCar Parts, etc and was told that because the car was relatively new that none of the after market manufacturers ( Bosal, etc ), weren`t producing them yet. Skoda OE only. Went to Skoda and asked for a price for the pipe and that i`d fit it myself and with the VAT it cam in at just under £400. That`s just the front section. I went home and chopped the exhaust off after the Cat, made a new piece and welded it on. Sorted. So if your system has a Cat that is part of the pipe then they may be quoting you for that as well?